There are numerous devices in the prior art whose primary function is to actuate means for deploying or inflating an air bag within a vehicle for restraint of the occupants in the event of a crash. Those devices which have been proposed for vehicles of the automotive type generally are arranged in some fashion to respond to an impact of the vehicle with an object, i.e., an impacted object which for purposes of background and description may be considered an obstruction or barrier or another vehicle, for example. In the prior art, generally it has been the practice to mount these devices on the vehicle in the region of and in association with the bumper. Therefore, upon impact in a crash environment followed by deformation or at least a yielding of the bumper, a sensing mechanism in the device will respond to actuate means for deployment of the air bag within the confines of the vehicle. The air bag so deployed then should be capable of carrying out its restraining function, i.e., to decelerate the forward momentum of the occupant following the crash. The ultimate aim or function of the air bag is to prevent or at least reduce the possibility of the occupant sustaining serious injury.
The prior art devices in large measure have not proved entirely satisfactory. One problem noted with many of these devices is that the speed of operation, i.e., the response time (T.sub.2 -T.sub.1) measured from the time at which there shall be an output (T.sub.2) minus the time of initial contact (T.sub.1), is not rapid enough. It should be apparent that the deployment of the air bag should occur within an extremely short time frame following a crash, otherwise there will be a diminution or loss of any safety factor since the occupant will have achieved a significant relative velocity with respect to the inside of the vehicle. The significance of response time and that there be a rapid response to the condition may be appreciated when it is considered, for example, that the bumper of a vehicle striking a barrier at 55 mph will be displaced approximately 3 inches in about 2.5 milliseconds time.
Another problem found to exist in many of these devices may be characterized as a general inability to prevent deployment of the air bag in a "low speed" crash. Normally, deployment of the air bag in a low speed crash environment would not be required for safety purposes and, further, the deployment of the air bag under these circumstances possibly could result in injury to the occupant. Another aspect of this problem is the inadvertent deployment of the air bag in a "g"-type sensing device. In such devices, it is not uncommon to obtain a response to ordinary shock, vibration or other sensations encountered in ordinary use of the vehicle. This aspect has its genesis in a difficulty in discriminating between a crash "signature" on the one hand and sensations such as ordinary shock and vibration on the other. Each vehicle has a slightly different "signature", the characteristic of which is dependent upon factors such as the nature of shock absorbers, undercoating and frame rigidity, to name a few. And, as the vehicle ages, the "signature" changes because of wear, aging and so forth of the equipment. This results in a greater difficulty in discrimination. Thus, the device must be tailored to the particular vehicle, but since over the life of the vehicle characteristics of such tailoring may change the response once obtained may not be obtainable during the life of the vehicle.
A further problem associated with certain prior art devices resides in complicated constructions and lack of universality of their adaption to vehicles both of standard size and those of smaller and lighter size which are gaining in popularity. Specifically, many of the known prior art devices for deploying an air bag are relatively large in size and weight. This is an important factor with many of the newer models.
One prior art device representative of a category of those above is described in U.S. Pat. No. 2,931,665 to Sander. The Sander device essentially includes an hydraulic system which actuates a switch in a crash environment. Problems and disadvantages associated with the Sander device include those related to or because of complication in construction and mode of operation, requiring several components, as well as its lack of universality in adaptation. A further disadvantage of the Sander device is perceived to reside in the fact that a fluid pump whose operation requires movement of the vehicle forms a part of the enabling apparatus. Accordingly, should the vehicle be stationary in a crash environment, the air bag would not be deployed.
Another prior art device, representative of a further category of those devices above, is described in U.S. Pat. No. 3,072,760 to Hazen. The Hazen device is dependent upon acceleration of the vehicle for deployment of an air bag. A shortcoming of the Hazen device and those of like nature is that it functions in dependence of a physical crushing of structure in a crash environment. Thus, the response time for the deployment of the air bag is determined, in part, by the particular physical properties of the obstruction. As a consequence, the device may not be actuated properly within the intended time interval should other than standard impacted objects be encountered.
Moreover, devices of this type suffer an additional disadvantage in that operation is dependent upon actual deformation of the vehicle during impact. And, if the device is to perform in the intended manner, it may of necessity require a specific construction for use with each vehicle type and model. Thus, this lack of universality renders these devices materially less versatile than might otherwise be possible.